Composite materials are composed of two or more physically distinct phases that produce properties different from the individual components. Composites can be very strong yet light weight. Examples include fiberglass, carbon fiber reinforced plastics, and cemented carbides. Composites find applications in aerospace, automotive, sports equipment due to their high strength to weight ratio and other advantageous properties. They are classified based on matrix material (polymer, metal, ceramic) and type of reinforcement (particles, fibers).

1. Composite Material
G.Gopinath
Assist.Prof - Mechanical

2. Composite Material Defined
A materials system composed of two or more physically
distinct phases whose combination produces aggregate
properties that are different from those of its constituents
Examples:
Cemented carbides (WC with Co binder)
Plastic molding compounds containing fillers
Rubber mixed with carbon black
Wood (a natural composite as distinguished from a synthesized
composite)

3. Why Composites are Important
Composites can be very strong and stiff, yet very light in
weight, so ratios of strength to weight and‑ ‑
stiffness to weight are several times greater than steel or‑ ‑
aluminum
Fatigue properties are generally better than for common
engineering metals
Toughness is often greater too
Composites can be designed that do not corrode like steel
Possible to achieve combinations of properties not attainable
with metals, ceramics, or polymers alone

4. Disadvantages and Limitations of
Composite Materials
Properties of many important composites are anisotropic ‑
the properties differ depending on the direction in which
they are measured – this may be an advantage or a
disadvantage
Many of the polymer based composites are subject to attack‑
by chemicals or solvents, just as the polymers themselves are
susceptible to attack
Composite materials are generally expensive
Manufacturing methods for shaping composite materials are
often slow and costly

5. One Possible Classification of
Composite Materials
Traditional composites – composite materials that occur in
nature or have been produced by civilizations for many years
Examples: wood, concrete, asphalt
Synthetic composites - modern material systems normally
associated with the manufacturing industries, in which the
components are first produced separately and then combined
in a controlled way to achieve the desired structure,
properties, and part geometry

6. Classification based on reinforcement

7. Classification based on
Matrix
 PMC – Polymer Matrix composites
 MMC – Metal Matrix composites
 CMC – Ceramic Matrix composites

8. Functions of the Matrix Material
(Primary Phase)
Protect phases from environment.
Transfer Stresses to phases.
When a load is applied, the matrix shares the load with the
secondary phase, in some cases deforming so that the stress is
essentially born by the reinforcing agent.

13. Materials for Fibers
Fiber materials in fiber reinforced composites:‑
Glass – most widely used filament
Carbon – high elastic modulus
Boron – very high elastic modulus
Polymers - Kevlar
Ceramics – SiC andAl2O3
Metals - steel
The most important commercial use of fibers is in polymer
composites

14. Fiber Reinforced Polymers‑
(FRPs)
A PMC consisting of a polymer matrix imbedded with
high strength fibers‑
Polymer matrix materials:
Usually a thermosetting (TS) plastic such as unsaturated
polyester or epoxy
Can also be thermoplastic (TP), such as nylons (polyamides),
polycarbonate, polystyrene, and polyvinylchloride
Fiber reinforcement is widely used in rubber products such as
tires and conveyor belts

15. Fibers in PMCs
Various forms: discontinuous (chopped), continuous, or
woven as a fabric
Principal fiber materials in FRPs are glass, carbon, and
Kevlar 49
Less common fibers include boron, SiC, andAl2O3, and
steel
Glass (in particular E glass) is the most common fiber‑
material in today's FRPs; its use to reinforce plastics dates
from around 1920

16. FRP Properties
High strength to weight and modulus to weight ratios‑ ‑ ‑ ‑
Low specific gravity - a typical FRP weighs only about 1/5 as
much as steel; yet, strength and modulus are comparable in fiber
direction
Good fatigue strength
Good corrosion resistance, although polymers are soluble in
various chemicals
Low thermal expansion - for many FRPs, leading to good
dimensional stability
Significant anisotropy in properties

17. FRP Applications
Aerospace – much of the structural weight of todays airplanes and
helicopters consist of advanced FRPs
Automotive – somebody panels for cars and truck cabs
Continued use of low-carbon sheet steel in cars is evidence of
its low cost and ease of processing
Sports and recreation
Fiberglass reinforced plastic has been used for boat hulls since
the 1940s
Fishing rods, tennis rackets, golf club shafts, helmets, skis, bows
and arrows.

18. Metal Matrix Composites (MMCs)
A metal matrix reinforced by a second phase
Reinforcing phases:
Particles of ceramic (these MMCs are commonly called
cermets)
Fibers of various materials: other metals, ceramics, carbon, and
boron

19. Cermets
MMC with ceramic contained in a metallic matrix
The ceramic often dominates the mixture, sometimes up to
96% by volume
Bonding can be enhanced by slight solubility between phases
at elevated temperatures used in processing
Cermets can be subdivided into
Cemented carbides – most common
Oxide based cermets – less common‑

20. Cemented Carbides
One or more carbide compounds bonded in a metallic matrix
The term cermet is not used for all of these materials, even though it is
technically correct
Common cemented carbides are based on tungsten carbide (WC),
titanium carbide (TiC), and chromium carbide (Cr3C2)
Tantalum carbide (TaC) and others are less common
Metallic binders: usually cobalt (Co) or nickel (Ni)

21. Applications
Space:The space shuttle uses boron/aluminum tubes to
support its fuselage frame. In addition to decreasing the
mass of the space shuttle by more than 145 kg,
boron/aluminum also reduced the thermal insulation
requirements because of its low thermal conductivity.The
mast of the HubbleTelescope uses carbon-reinforced
aluminum.

22. Military: Precision components of missile guidance systems
demand dimensional stability — that is, the geometries of
the components cannot change during use. Metal matrix
composites such as SiC/aluminum composites satisfy this
requirement because they have high microyield strength.
In addition, the volume fraction of SiC can be varied to
have a coef cient of thermal expansion compatible withfi
other parts of the system assembly.
Applications

23. Transportation: Metal matrix composites are nding usefi
now in automotive engines that are lighter than their metal
counterparts.Also, because of their high strength and low
weight, metal matrix composites are the material of choice
for gas turbine engines.
structural applications, the matrix is usually a lighter
metal such as aluminum, magnesium, or titanium, and
provides a compliant support for the reinforcement.
Applications

24. Other Composite Structures
Laminar composite structure – conventional
Sandwich structure
Honeycomb sandwich structure